This invention relates to the coating of glass and, in particular, to an apparatus for coating glass with boron as a protective coating over another coating material.
A variety of coating materials have been used or have been proposed for modifying the radiation transmission and reflection characteristics of glass, for enhancing the appearance of glass, or for providing decorative patterns on a glass surface. Such coatings often serve more than one purpose. For example, metal oxide coatings and vacuum-evaporated metal coatings have been used to endow glass with solar control properties while at the same time giving the glass an attractive hue. However, many coating materials having desired properties are sensitive to chemical and/or mechanical damage encountered during use and a protective coating is required.
For example, boron has been found to be a good protective coating for titanium nitride used as a coating material on glass. Boron deposits are very hard and can not be penetrated by abrasive cleaners. Also, chemical resistance to acids and alkalis is outstanding. Boron is easily deposited from diborane, its simplist hydride, but the decomposition of diborane is exceedingly rapid and is temperature sensitive. Thus, previously known vapor deposition beams, such as the apparatus disclosed in U.S. Pat. No. 4,088,471, can not be successfully utilized to deposit boron.